Microelectronic devices, such as semiconductor devices, imagers and displays, are generally fabricated on and/or in microelectronic workpieces using several different types of machines (“tools”). Many such processing machines have a single processing station that performs one or more procedures on the workpieces. Other processing machines have a plurality of processing stations that perform a series of different procedures on individual workpieces or batches of workpieces. In a typical fabrication process, one or more layers of conductive materials are formed on the workpieces during deposition stages. The workpieces are then typically subject to etching and/or polishing procedures (i.e., planarization) to remove a portion of the deposited conductive layers for forming electrically isolated contacts and/or conductive lines.
Tools that plate metals or other materials onto workpieces are becoming an increasingly useful type of processing machine. Electroplating and electroless plating techniques can be used to deposit copper, solder, permalloy, gold, silver, platinum, electrophoretic resist and other materials onto workpieces for forming blanket layers or patterned layers. A typical copper plating process involves depositing a copper seed layer onto the surface of the workpiece using chemical vapor deposition (CVD), physical vapor deposition (PVD), electroless plating processes, or other suitable methods. After forming the seed layer, a blanket layer or patterned layer of copper is plated onto the workpiece by applying an appropriate electrical potential between the seed layer and an anode in the presence of an electroprocessing solution. The workpiece is then cleaned, etched and/or annealed in subsequent procedures before transferring the workpiece to another processing machine.
Conventional single-wafer processing stations generally include a container for receiving a flow of electroplating solution from a fluid inlet. The processing station can include an anode, a plate-type diffuser having a plurality of apertures, and a workpiece holder for carrying a workpiece. The workpiece holder can include a plurality of electrical contacts for providing electrical current to a seed layer on the surface of the workpiece. When the seed layer is biased with a negative potential relative to the anode, it acts as a cathode. In operation, the electroplating fluid flows around the anode, through the apertures in the diffuser, and against the plating surface of the workpiece. The electroplating solution is an electrolyte that conducts electrical current between the anode and the cathodic seed layer on the surface of the workpiece. Therefore, ions in the electroplating solution plate the surface of the workpiece.
The plating machines used in fabricating microelectronic devices must meet many specific performance criteria. For example, many plating processes must be able to form small contacts in vias or trenches that are less than 0.5 μm wide, and often less than 0.1 μm wide. A combination of organic additives such as “accelerators,” “suppressors,” and “levelers” can be added to the electroplating solution to improve the plating process within the trenches so that the plating metal fills the trenches from the bottom up. As such, maintaining the proper concentration of organic additives in the electroplating solution is important to properly fill very small features.
One drawback of conventional plating processes is that the organic additives decompose and break down proximate to the surface of the anode. Also, as the organic additives decompose, it is difficult to control the concentration of organic additives and their associated breakdown products in the plating solution, which can result in poor feature filling and nonuniform layers. Moreover, the decomposition of organic additives produces by-products that can cause defects or other nonuniformities. To reduce the rate at which organic additives decompose near the anode, other anodes such as copper-phosphorous anodes can be used.
Another drawback of conventional plating processes is that organic additives and/or chloride ions in the electroplating solution can passivate and/or consume pure copper anodes. This alters the electrical field, which can result in inconsistent processes and nonuniform layers. Thus, there is a need to improve the plating process to reduce the adverse effects of the organic additives.
One existing approach to inhibit organic additives from contacting and passivating the anode is to place a porous barrier between the workpiece and the anode. This approach, however, only reduces the number of additives that decompose proximate to the anode surface. Furthermore, approaches that utilize a barrier to separate the workpiece from the anode can create chemical imbalances in the electroplating solution such that the concentration of one or more of the constituents in the solution is outside of the desired operating range. When the concentration of a component of the electroplating solution is not within the operating range, the plating process may be unsustainable and the processing fluid may need to be replaced. Thus, chemical imbalances can adversely affect the plating process and increase the frequency with which the electroplating solution must be replaced.